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Bulging biceps get their power from a mesh arrangement of cells rather than long ropes, detailed studies reveal.

As muscles flex, tugging filaments fan out in a lattice, say the University of Washington team who made the breakthrough. And it’s not just biceps that use this force - all muscles, including the heart, appear to do it.

The news will be of interest to bodybuilders who strive to maximise their muscle power, but could also help doctors treating heart problems.